1. Field of the Invention
The present invention relates to a brake pipe, a fuel pipe or the like for use with an automobile, especially a metallic pipe of a comparatively small diameter of less than 20 mm arranged below the body of the automobile and more particularly to a connecting structure of the small-diameter metallic pipe with respect to a mating member such as an end metal or joint, with the metallic pipe having the outer peripheral surface thereof covered with at least a thick film-like resin layer so as to have a corrosion-resistant property against chipping or splashing during traveling of the automobile and being subjected to an end processing such as the formation of a flare, a spool or a bulge at one end of the pipe by assembling a clamp nut by a after-processing.
2. Description of Prior Art
Recently, a number of resin-coated metallic pipes have been proposed for brake pipes, fuel pipes and other pipes arranged below an automobile so as to allow these pipes to have an anti-chipping property or anti-splashing property.
As such resin-coated metallic pipes, there have conventionally been known one that is provided with a polymeric coating layer formed such that a chromate film is formed according to necessity on a Zn or Zn/Ni film plated on the outer surface of a metallic pipe, then polyvinyl fluoride (PVF) is coated on the chromate film to a thickness of about 20 .mu.m and a heat contractible tube is caused to cover the entire length of the chromate film to thereby form a polymeric coated layer and one that is formed such that a Zn or Zn/Al plated film is formed on the outer peripheral surface of a metallic pipe according to an electrical, chemical or hot-dipping method and a polyamid type resin (PA) such as PA11 or PA12 of a thickness of about 200-300 .mu.m is extrusion-molded on the plated film.
However, in the conventional technology for manufacturing the first-mentioned conventional tube, since an expensive heat contractible tube is used over the entire length of the pipe, the manufacturing cost increases and further, since the technology includes the step of contracting the entire length of the tube after covering the heat contractible tube with the polyvinyl fluoride layer, much time and labor are required for manufacturing the tube thereby reducing productivity while the second mentioned conventional technology for manufacturing the tube, since the tube makes use of a thick film-like polyamide type resin as a single layer, when the tube is subjected to chipping or the like, the problem has arisen that the corrosion-resistant property of the pipe deteriorates.
Therefore, the present applicant proposed a metallic pipe having a surface treatment layer consisting of a plated film such as Zn was polymerously covered with a first layer and a second layer of which the first layer consisted of an adhesive and extrusion-moldable thin film-like polyamide type resin and the second layer consisted of an anti-chipping and extrusion-moldable thick film-like resin such as polypropylene, polyethylene or the above-mentioned polyamide type resin and laid over the first layer. (refer to Japanese Patent Application H9-145869). This polymeric coated metallic pipe has excellent characteristics that it has an excellent corrosion--resistant property without spoiling its anti-chipping and anti-splashing properties and it can be manufactured with ease.
In the case of the above-described polymerized coated metallic pipe, the pipe must be provided with a resin-uncovered portion required for performing a pipe end processing for enabling a clamp nut to be assembled to the metallic pipe and the formation of a flare, spool or bulge for the purpose of connecting the mating member such as an end metal or a joint to the pipe. Such resin-uncovered portion is required to have a clamp nut assembled thereto for its connection with a mating member such as a joint and has its one end press-worked by punch while causing the pipe end to be slightly projected so as to be held by a chuck for punch shaping so that it is necessary to secure at least a total length of the clamp nut, a chuck margin and a shaping margin. Accordingly, the resin uncovered portion is usually provided to a length of about 50-140 mm from the pipe end to be processed. Further, for the provision of such resin-uncovered portion, there is a method of peeling the thick film-like resin layer by an after-processing or a method for covering a pipe with a thick film-like resin layer over the entire length of the outer peripheral surface of the pipe with the exception of at least the pipe end corresponding to the working margin required during the manufacturing process.
Then, where the metallic pipe with its one end having a resin-uncovered portion and subjected to an end processing is connected to a mating member, a clamp nut 21 assembled to the resin-uncovered portion at one end of the pipe is screw-fitted into a screw-threaded portion 21-1 of a joint 22 as the mating member so that a double-flare portion 23-1 formed as a result of end processing is connected by being brought into contact with a sheet-surface 22-2 of the joint 22, as shown in FIG. 15 as an example of a connecting structure. Further, FIG. 16 illustrates a connecting structure using a cap type clamp nut 21 instead of the male type clamp nut shown in FIG. 15 and in this case, the cap type clamp nut 21 is screw-fitted into the screw-threaded portion 22-1 of the joint 22 as the mating member and then clamped so that both members are connected to each other through contact of the end-processed double flare 23-1 of the metallic pipe 23 with the sheet surface 22-2 of the joint 22. Further, a connection structure example shown in FIG. 17 makes use of an O-ring flare 23-1a in place of the above-mentioned double flare section 23-1 thereby securing the sealing property by interposing an O-ring 25 between the sheet surface 22-2 and the O-ring flare 231-1a and this case also indicates a system in which the clamp nut 21 assembled to the resin-uncovered portion is screw-fitted into, and clamped to, the screw-threaded portion 22-1 of the joint 22 as a mating member.
However, in the case of such connecting structure, as will be clear from the drawings, due to the presence of the above-mentioned chuck margin and the movement of the clamp nut 21 toward the double flare portion 23-1 or the O-ring flare 23-1a following the screw-fitting of the joint 22 into the screw-threaded portion 22-1, the resin-uncovered portion becomes widely exposed between the rear end surface 21-1 of the clamp nut 21 and the end surface 24-1 of the outer resin-coated layer 24. If this exposed resin-uncovered portion is left as it is, there is the possibility of that portion becoming damaged by chipping or muddy water or of causing deterioration of the corrosion-resistant property due to the possible generation of cracks so that it has been necessary to take some countermeasure against it.